1. Field of the Invention
The invention relates to an accessory drive apparatus, and more particularly to a driving mechanism for an accessory system for driving a power source, such as a fuel cell system.
2. Description of Related Art
Japanese Laid-open Patent Publication No. 6-229447 discloses a transmission device for transmitting rotary power of an engine to an engine accessory while changing the speed of rotation, so as to drive the engine accessory. The transmission device disclosed in this publication includes a hollow rotating member, a first gear, a second gear, and a clutch. The hollow rotating member, which is rotatably supported on a drive shaft of the accessory, has an input engaging portion formed at an outer circumferential surface thereof, and a planetary gear rotatably attached to an inner circumferential surface thereof. In operation, the rotary power is transmitted from the engine to the input engaging portion of the hollow rotating member. The first gear is fixedly attached to the drive shaft of the accessory, and meshes with the planetary gear in the hollow rotating member. The second gear is freely rotatably attached to the drive shaft of the accessory, and meshes with the planetary gear in the hollow rotating member. The clutch engages/disengages a stationary or fixed portion of the accessory with/from the second gear, so as to apply braking force to the second gear. When the clutch is in the released or unengaged state, rotation of the second gear is not restricted, and only the revolution of the planetary gear around the drive shaft contributes to rotation of the hollow rotating member, whereby the accessory rotates at the same speed in the same direction as the hollow rotating member. When the clutch is in the engaged state, on the other hand, rotation of the second gear is restricted, and the first gear is rotated at an increased rotational speed achieved by adding the rotation of the planetary gear on its own axis to the revolution thereof around the drive shaft of the accessory. As a result, the accessory rotates at an increased speed as compared with the speed of rotation of the hollow rotating member. By suitably controlling the engaging state of the clutch, therefore, the rotational speed of the accessory can be controlled as desired.
In the above-described arrangement in which the driving force applied to the accessory is controlled or adjusted by means of the clutch, loss of power is caused by so-called clutch slipping when the clutch is in an intermediate slipping state between a fully engaged position and a fully released position, resulting in a reduced efficiency in driving the accessory.
Another driving source may be installed for driving an accessory or accessories. In this case, however, the driving source must be large-sized so as to provide sufficiently large power or driving force, resulting in an increased cost. In particular, while fuel-cell vehicles have been increasingly developed in recent years, a system for driving an accessory or accessories for a fuel cell system, which requires a large number of motors and inverters, is undesirably large-sized and complicated in construction. Thus, it has been considered important to simplify the system for driving the accessory.